1. Field of the Invention
The present invention relates to a magnetic recording medium such as a magnetic recording disk incorporated within a hard disk drive (HDD), for example.
2. Description of the Prior Art:
In general, a magnetic layer for recordation is layered on the surfaces of a substrate in a magnetic recording disk. The magnetic layer may include magnetic crystal grains formed based on cobalt (Co) atoms. As conventionally known, chromium (Cr) atoms are usually forced to diffuse along the boundaries between the adjacent ones of the magnetic crystal grains in the magnetic layer. This local diffusion of the Cr atoms serves to generate non-magnetic walls between the adjacent magnetic crystal grains. The Cr non-magnetic walls function to prevent the magnetic interaction between the adjacent magnetic crystal grains. The prevention of the magnetic interaction between the adjacent magnetic crystal grains in this manner reduces noise in reading out magnetic bit data from the magnetic recording disk.
The size of the magnetic crystal grains should be minimized to improve the recording density in the magnetic layer. It is well known that reduction in the thickness of the magnetic layer leads to minimization of the magnetic crystal grains. However, a reduced thickness of the magnetic layer inevitably induces a reduction in tBr, the product of thickness and residual magnetization, so that the intensity is reduced in the magnetic field leaking out of the magnetic layer. It is accordingly difficult to obtain the magnetic output of a sufficient magnitude. In addition, a reduced thickness of the magnetic layer is accompanied with a reduction in the coercivity Hc. If the coercivity Hc gets reduced, the magnetic bit data on the magnetic layer tends to get broken due to a thermal disturbance or the like.